In general, a liquid crystal display employs an alternating current (AC) driving system that alternately applies driving voltages of positive polarity and negative polarity to liquid crystal elements of each pixel for each one frame or each one horizontal period, in order to suppress deterioration of the liquid crystal. Further, the apparatus is driven in such a way as to invert the polarities of adjacent data lines or scanning lines, in order to suppress flicker that occurs due to the AC driving system.
FIG. 1 is a partially-broken perspective diagram of a conventional active matrix type liquid crystal display. FIG. 2 is a cross-section of key portions of the conventional active matrix type liquid crystal display. As shown in FIG. 1 and FIG. 2, in the conventional liquid crystal display, pixel electrodes 11 and TFT's 12 as switching elements are disposed in a matrix shape of m rows and n columns on a substrate (“TFT substrate”) 1. Electrodes that are common (“common electrodes”) 21 are uniformly provided substantially on the whole surface a substrate (“common substrate”) 2. A liquid crystal layer 3 is sealed into between the TFT substrate 1 and the common substrate 2 by a sealing section 31. A plurality of data lines 13 and a plurality of scanning lines 14 are provided in lengthwise and crosswise on the TFT substrate 1, and the TFT's 12 are connected to these points of intersection.
According to a liquid crystal display that uses polysilicon TFT's as switching elements, usually, a part of or the whole driving circuit of the data lines 13 or the scanning lines 14 are manufactured on the TFT substrate 1, as the carrier mobility of the polysilicon TFT's is large. As shown in FIG. 1, a data line driving circuit 15 and a scanning line driving circuit 16 are provided on the TFT substrate 1. An electrode 17 that becomes an outgoing line is provided on the peripheral area of the TFT substrate 1. A common electrode voltage is applied to the common electrodes 21 via this electrode 17 and a conductor (a transfer) 18 that is connected to this electrode 17. The electrode 17 is covered with a protection film 19.
As an AC driving system of this liquid crystal display, there is a common fixed driving system that fixes a common electrode voltage to a constant value. According to this driving system, a voltage that has positive polarity and a voltage that has negative polarity relative to the common electrode voltage respectively are applied alternately to the data lines 13. In other words, the polarity of the voltage applied to the data lines 13 is inverted. As the amplitude of the voltage applied to the data lines 13 becomes large, the power source voltage of the data line driving circuit 15 becomes large. As a result, a withstanding voltage that is required for transistors, buffers, and analog switches of the data line driving circuit 15 becomes large. Further, power consumption also increases.
There is also a driving system (a common inversion driving system) that minimizes the amplitude of a voltage supplied to the data line 13, by inverting the polarity of the common electrode voltage. For example, the amplitude of a voltage applied to the data lines 13 is restricted to a range of within 5 V, and the common electrode voltage is changed to match the polarity inversion period. Based on this, it becomes possible to restrict the power source voltage of the data line driving circuit 15 to 5 V, for example. Therefore, it is possible to lower the withstanding voltage and the power consumption of the elements of the data line driving circuit 15, which is advantageous in the aspect of cost and power consumption.
However, according to the conventional liquid crystal display, the load becomes large when the sizes of the screen become large, as the common electrode 21 are provided uniformly substantially on the whole surface of the common substrate 2. Therefore, the conventional liquid crystal display has had a problem that it is difficult to inversely drive the common electrodes 21, and that flicker also occurs.